1. Field of the Invention
The present invention relates to an electrically operated braking system of a motor vehicle, which includes a brake employing an electric motor as a drive source.
2. Discussion of the Related Art
An electrically operated braking system of a motor vehicle generally includes (a) a brake operating member such as a brake pedal, which is operated by an operator of a motor vehicle, (b) an electric power source such as a battery, (c) a brake including an electric motor which is operated by an electric power supplied from the electric power source, to generate a drive force for forcing a friction member onto a rotor rotating with a wheel of the vehicle, for thereby braking the wheel, and (d) a controller which determines an amount of the electric power to be supplied from the electric power source to the electric motor, depending upon an operating amount of the brake operating member, for thereby controlling an operation of the brake.
A friction coefficient of friction members such as brake pads or brake linings used in a brake generally varies due to gradual deterioration or wearing of the friction members, or due to temperature or humidity of the friction members. Further, the friction members have different friction coefficient values due to variations associated with the manufacture. In an electrically operated braking system as described above, a change in the friction coefficient of the friction members will cause a change in the relationship between the amount of electric power actually supplied from the electric power source to the electric motor of the brake and the braking torque actually applied from the brake to the corresponding wheel. In other words, the relationship between the amount of electric power supplied to the motor and the braking torque generated by the brake is not necessarily held constant.
However, the conventional electrically operated braking system does not obtain and utilize the actual relationship between the supplied amount of electric power and the braking torque generated by the brake. That is, the conventional system uses a predetermined nominal relationship between the electric power amount and the braking torque, to determine the amount of electric power to be supplied to the electric motor, depending upon the operating amount of the brake operating member, on the assumption that the relationship is held constant. Therefore, the conventional electrically operated braking system is not capable of accurately controlling the braking torque of the brake in relation to the operating amount of the brake operating member.
It is an object of this invention to provide an electrically operated braking system which obtains an actual relationship between the amount of electric power supplied to an electric motor and the braking torque generated by the brake, and utilizes the obtained relationship.
The above object may be achieved according to any one of the following modes or embodiments of the present invention, which are numbered to indicate possible combinations of various features of the invention:
(1) An electrically operated braking system of a motor vehicle having a wheel, comprising: (a) a rotor rotating with the wheel; (b) a brake operating member which is operated by an operator of the motor vehicle; (c) an electric power source; (d) a brake including a friction member movable to be forced onto the rotor, and an electric motor which is operated by an electric power supplied from the electric power source, to generate a drive force for forcing the friction member onto the rotor and thereby braking the wheel; and (e) a controller which determines an amount of the electric power to be supplied from the electric power source to the electric motor, depending upon an operating amount of the brake operating member, for thereby controlling an operation of the brake, the braking system being characterized by further comprising (e) a relationship estimating and utilizing device for obtaining an actual value of the electric power supplied from the electric power source to the electric motor during an operation of the brake while the motor vehicle is running, and an actual value of a braking torque applied from the brake to the wheel during the operation of the brake. The relationship estimating and utilizing device is adapted to estimate a relationship between the electric power to be supplied to the electric motor and the braking torque to be applied to the wheel, on the basis of the actual values obtained, and utilize the relationship. The relationship is formulated such that the braking torque to be applied to the wheel is changed with a change in the electric power to be supplied to the electric motor.
In the braking system constructed according to the above mode (1) of the present invention, the relationship estimating and utilizing device is capable of obtaining the relationship between the electric power to be supplied to the electric motor of the brake and the braking torque to be applied from the brake to the wheel. The relationship estimating and utilizing device is further adapted to utilize the obtained relationship for various purposes, for instance, for controlling the brake and providing the vehicle operator with information helpful to operate the vehicle.
The electric power to be applied to the electric motor may be expressed by a voltage or current. The electric motor of the brake may be a ultrasonic motor or DC motor. The operating amount of the brake operating member may be expressed as an operating force acting on the brake operating member, or an operating stroke or distance of the brake operating member. The operation of the brake while the vehicle is running may be a normal operation initiated by an operation of the brake operating member by the vehicle operator, or a special operation which is performed without an operation of the brake operating member, for the sole purpose of estimating the above-indicated relationship.
(2) An electrically operated braking system according to the above mode (1), wherein said relationship is a pattern of change of said braking torque with a change of said electric power, and said relationship estimating and utilizing device comprises relationship estimating means for selecting one of a plurality of candidate patterns which corresponds to a combination of the actual values obtained during the operation of the brake while the motor vehicle is running.
(3) An electrically operated braking system according to the above mode (2), wherein said relationship estimating means includes pattern memory means for storing the above-indicated plurality of candidate patterns, and pattern selecting means for selecting the above-indicated one of the plurality of candidate patterns stored in the pattern memory means.
(4) An electrically operated braking system according to any one of the above modes (1)-(3), wherein the relationship estimating and utilizing device obtains the above-indicated relationship from a plurality of different relationships between the electric power to be supplied to the electric motor and the braking torque to be applied to the wheel.
In the braking system according to the above mode (4), the control load of the relationship estimating and utilizing device is made smaller than in the braking system in which the relationship is estimated in a continuous fashion.
(5) An electrically operated braking system according to any one of the above modes (1)-(4), wherein the controller includes the relationship estimating and utilizing device, and the relationship estimating and utilizing device includes relationship utilizing means for determining a desired value of the braking torque on the basis of the operating amount of the brake operating member, and determining the value of the electric power to be supplied to the electric motor, on the basis of the determined desired value of the braking torque and according to the estimated relationship.
In this braking system, the electric power to be supplied to the electric motor during an operation of the brake is determined according to the actual relationship between the electric motor and the braking torque, as well as depending upon the operating amount of the brake operating member, so that the brake can be accurately controlled so as to provide the braking torque corresponding to the operating amount of the brake operating member, irrespective of a variation in the friction coefficient of the friction members used in the brake.
(6) An electrically operated braking system according to any one of claims 1-5, wherein the relationship estimating and utilizing device includes means for supplying a predetermined amount of the electric power from the electric power source to the electric motor for a predetermined length of time to thereby activate the brake while the motor vehicle is running without an operation of the brake operating member, and obtaining the actual values of the electric power and the braking torque during activation of the brake.
In the braking system according to the above mode (6), the brake is activated for the sole purpose of estimating the relationship, while the brake operating member is not in operation, that is, while the vehicle is running under a condition that does not require a normal operation of the brake. Since the relationship is estimated in this condition without an operation of the brake operating member, the accuracy of estimation of the relationship is made relatively high.
In a usual run of the motor vehicle, the relationship estimating and utilizing device is operated to activate the brake for estimating the relationship, prior to a normal operation of the brake by an operation of the brake operating member by the vehicle operator. Accordingly, the estimated actual relationship between the electric power to be supplied to the electric motor of the brake and the braking torque to be generated by the brake can be utilized to control the brake upon initial activation of the brake during the vehicle run.
While the actual value of the braking torque generated by the brake with the predetermined amount of the electric power supplied to the electric motor is obtained while the brake operating member is not in operation, the estimation of the relationship on the basis of the above-indicated predetermined amount of the electric power and the obtained braking torque may be effected either immediately after the actual braking torque value is obtained during running of the vehicle without an operation of the brake operating member, or during the next normal operation of the brake initiated by an operation of the brake operating member.
(7) An electrically operated braking system according to the above mode (6), wherein the means for supplying the predetermined amount of the electric power to the electric motor for the predetermined length of time while the vehicle is running without an operation of the brake operating member comprises a brake operation detecting sensor for detecting an operation of the brake operating member, and a vehicle run detecting sensor for detecting a running of the vehicle, and activates the brake by supplying the predetermined amount of the electric power to the electric motor when the above sensors detect that the vehicle is running without an operation of the brake operating member.
(8) An electrically operated braking system according to the above mode (6) or (7), wherein the motor vehicle has a front left wheel and a front right wheel, and the braking system comprises the brake for each of the front left and right wheels, and wherein the means for supplying the predetermined amount of the electric power to the electric motor while the vehicle is running without an operation of the brake operating member is adapted to concurrently activate the brakes for the two front wheels.
In this braking system wherein the brakes for the front left and right wheels are concurrently activated while the vehicle is running without an operation of the brake operating member, the same amounts of the electric power are preferably applied to the electric motors for the two front brakes to generate the same braking torque, so as to avoid generation of a yaw moment acting on the vehicle body during activation of the front brakes by the relationship estimating and utilizing device. This arrangement is effective to prevent yawing of the vehicle during activation of the front brakes by the relationship estimating and utilizing device, which may be felt unusual or abnormal by the vehicle operator.
(9) An electrically operated braking system according to any one of the above modes (6)-(8), wherein the motor vehicle has a front wheel and a rear wheel, and the braking system comprises the brake for each of the front and rear wheels, and wherein the means for supplying the predetermined amount of the electric power to the electric motor while the motor vehicle is running without an operation of the brake operating member is adapted to activate the brakes for the front and rear wheels at different times.
In the braking system according to the above mode (9) wherein the deceleration value of the vehicle body during activation of the brake for each of the front and rear wheels is made lower than in the braking system wherein the brakes for the front and rear wheels are activated concurrently. This arrangement makes it possible to estimate the relationship without the vehicle operator feeling unusual or uncomfortable with excessive deceleration of the vehicle while the vehicle is running without an operation of the brake operating member. Further, the predetermined amount of the electric power to be supplied to the electric motor of the brake for each of the front and rear wheels can be increased to improve the accuracy of estimation of the relationship, because the two brakes for the front and rear wheels are activated at different times, with the relatively low deceleration value of the vehicle body during activation of each brake.
(10) An electrically operated braking system according to any one of the above modes (6)-(9), wherein said means for supplying the predetermined amount of the electric power to the electric motor while the vehicle is running without an operation of the brake operating member is operated to activate the brake only once during a run of the motor vehicle, to obtain the actual value of the braking torque to be applied to the wheel.
(11) An electrically operated braking system according to the above mode (10), further comprising a vehicle start member which is operated by the vehicle operator when the run of the vehicle is initiated, and wherein the means for supplying the predetermined amount of the electric power to the electric motor determines, upon operation of the vehicle start member, that the run of the vehicle has been initiated.
(12) An electrically operated braking system according to any one of the above modes (1)-(11), wherein the relationship estimating and utilizing device comprises standard relationship utilizing means for provisionally utilizing a predetermined standard relationship stored in a memory, before said relationship is estimated for the first time during a run of the motor vehicle on the basis of the actual values of the electric power and braking torque which are obtained during activation of the brake without an operation of the brake operating member.
(13) An electrically operated braking system according to any one of the above modes (1)-(11), wherein the relationship estimating and utilizing device stores in a memory the relationship which is estimated during each run of the motor vehicle, and before the relationship is estimated during a present run of the vehicle, provisionally utilizes the relationship which was obtained during the preceding run of the motor vehicle and which is stored in the memory.
In the braking system according to the above mode (13), the stored relationship obtained during the preceding run of the vehicle is provisionally utilized until the relationship is obtained during the present run of the vehicle. The relationship which was actually obtained during the preceding run of the vehicle is more reliable than the standard relationship which is not actually obtained.
(14) An electrically operated braking system according to any one of the above modes (1)-(5), wherein the relationship estimating and utilizing device comprises means for obtaining the actual values of the electric power supplied to the electric motor and the braking torque generated by the brake activated while the vehicle is running with an operation of the brake operating member, and estimates the relationship on the basis of the above-indicated actual values.
The braking system according to the above mode
(14) may include the feature according to any one of the above modes (11), (12) and (13).
(15) An electrically operated braking system according to any one of the above modes (1)-(14), further comprising a driver connected between the electric power source and the electric motor so that the electric power is supplied from the electric power source to the electric motor through the driver according to an external control command applied to the driver, and the relationship estimating and utilizing device comprising electric power estimating means for estimating the actual value of the electric power supplied from the electric power source to the electric motor, on the basis of the external control command, and for estimating the relationship on the basis of the estimated actual value of the electric power.
The braking system according to the above mode (15) does not require an electric power sensor for detecting the electric power actually supplied to the electric motor, since the actual value of the electric power supplied to the electric motor is estimated from the control command applied to the driver. Where the relationship estimating and utilizing device comprises the means for suppling the predetermined amount of the electric power to the electric motor while the vehicle is running without an operation of the brake operating member, as described above with respect to the mode (5) of this invention, this means applies the control command to the driver. Where the relationship estimating and utilizing device comprises means for obtaining the actual values of the electric power supplied to the electric motor and the braking torque generated by the brake activated while the vehicle is running with an operation of the brake operating member, as described above with respect to the mode (14) of this invention, the controller for the brake applies the control command to the driver.
(16) An electrically operated braking system according to any one of the above modes (1)-(14), wherein the relationship estimating and utilizing device comprises an electric power sensor for detecting the electric power actually supplied to the electric motor, and estimates the relationship on the basis of the actual value of the supplied electrical power detected by the electric power sensor.
The value of the electric power represented by the control command applied to the driver is not necessarily equal to the value of the electric power actually supplied to the electric motor. Further, the value of the electric power actually supplied to the electric motor may vary with a change in the load of the electric motor, even when the same control command is applied to the driver. Therefore, the actual value of the electric power supplied to the electric motor may not be estimated with high accuracy in the braking system according to the above mode (15). In this respect, the braking system according to the above mode (16) in which the actually supplied electric power is detected by the sensor permits improved accuracy of estimation of the actual relationship between the electric power to be supplied to the electric motor and the braking torque to be generated by the brake.
(17) An electrically operated braking system according to any one of the above modes (1)-(16), wherein the relationship estimating and utilizing device comprises a braking torque sensor for detecting the actual value of the braking torque applied from the brake to the wheel, and estimates the relationship on the basis of the actual value of the braking torque detected by the braking torque sensor.
(18) An electrically operated braking system according to any one of the above modes (1)-(16), wherein the relationship estimating and utilizing device includes vehicle deceleration detecting means for detecting a deceleration value of the motor vehicle, and obtains the actual value of the braking torque on the basis of the deceleration value detected by the vehicle deceleration detecting means.
In the braking system according to the above mode (18), the actual value of the braking torque is obtained on the basis of the detected deceleration value of the vehicle, based on a fact that the vehicle deceleration value increases with an increase in the actual braking torque. In this respect, it is also noted that the vehicle deceleration value can be detected more easily than the actual braking torque. That is, the actual value of the braking torque can be obtained relatively easily on the basis of the detected vehicle deceleration value.
The vehicle deceleration detecting means may be adapted to directly detect the deceleration value of the vehicle body, or may be a combination of a vehicle speed sensor for detecting the running speed of the vehicle, and means for calculating the deceleration value of the vehicle based on the detected vehicle running speed. Alternatively, the vehicle deceleration detecting means may comprise wheel speed sensors for detecting rotating speeds of a plurality of wheels of the motor vehicle, vehicle speed estimating means for determining as an estimated vehicle running speed a highest one of the wheel speeds detected by the respective wheel speed sensors (on the basis of a fact that the highest wheel speed is closest to the actual running speed of the vehicle), and vehicle deceleration calculating means for calculating the deceleration value of the vehicle on the basis of the estimated vehicle running speed.
(19) An electrically operated braking system according to any one of the above modes (1)-(16), wherein the relationship estimating and utilizing device comprises vehicle deceleration detecting means for detecting a deceleration value of the motor vehicle while a gradient of a road surface on which the motor vehicle is running is substantially zero, and obtains the actual value of the braking torque on the basis of the deceleration value detected by the vehicle deceleration detecting means.
While the vehicle deceleration value increases with an increase in the actual braking torque, as described above, the vehicle deceleration value may vary with the gradient of the road surface, even when the actual braking torque is kept constant. Based on this fact, the vehicle deceleration detecting means used in the braking system according to the above mode (19) is adapted to detect the vehicle deceleration value while the road surface gradient is substantially zero, and the relationship estimating and utilizing means is adapted to obtain the actual braking torque based on the vehicle deceleration value detected while the road surface gradient is substantially zero. Thus, the actual braking torque can be obtained with high accuracy based on the detected vehicle deceleration value.
(20) An electrically operated braking system according to any one of the above modes (1)-(16), wherein the relationship estimating and utilizing device includes a wheel speed sensor for detecting a rotating speed of the wheel, obtains a deceleration value of the wheel on the basis of a rate of change of the rotating speed of the wheel detected by the wheel speed sensor, and obtains the actual value of the braking torque on the basis of the deceleration value of the wheel obtained.
In the braking system according to the above mode (20), the actual value of the braking torque is obtained on the basis of the detected deceleration value of the vehicle wheel, based on a fact that the wheel deceleration value increases with an increase in the actual braking torque. In this respect, it is also noted that the wheel deceleration value can be detected more easily than the actual braking torque. That is, the actual value of the braking torque can be obtained relatively easily on the basis of the detected wheel deceleration value.
Where the braking system comprises a plurality of brakes for respective wheels, the deceleration value of the vehicle is influenced by the braking effects provided by all or some of the brakes which are activated. Therefore, it is difficult to accurately obtain the actual braking effect of the brake for each wheel based on the deceleration value of the vehicle. In the braking system according to the above mode (20), however, the actual braking torque generated by the brake for each wheel can be accurately obtained on the basis of the rate of change of the rotating speed of the wheel. According to this arrangement, the relationship between the electric power to be supplied to the electric motor and the braking torque to be generated by the brake can be estimated for each of the plurality of wheels, so that the estimated relationship can be utilized for controlling the brake for each wheel, depending upon the specific condition of each brake.
(21) An electrically operated braking system according to the above mode (6) or (7), wherein the brake is provided for each of a plurality of wheels provided for the motor vehicle, and the means for supplying the predetermined amount of the electric power to the electric motor while the motor vehicle is running without an operation of the brake operating member is adapted to activate the brakes for the respective wheels at different times, detect the deceleration values of the motor vehicle during the activation of the respective brakes, and obtain the actual value of the braking torque of each brake on the basis of the vehicle deceleration value detected during the activation of that brake.
In the braking system according to the above mode (21) wherein the brakes for the respective wheels are activated at different times during running of the motor vehicle without an operation of the brake operating member, the vehicle deceleration values are detected during the activation of the respective brakes. In this arrangement, the vehicle deceleration value detected during activation of a given one of the brakes reflects only the actual braking torque generated by that brake. Thus, the actual braking torque of each brake can be accurately obtained based on the vehicle deceleration value detected during operation of that brake, and the relationship can be obtained for each of the brakes.
(22) An electrically operated braking system according to the above mode (6) or (7), wherein the brake is provided for each of a front wheel and a rear wheel provided for the motor vehicle, and the means for supplying the predetermined amount of the electric power to the electric motor while the motor vehicle is running without an operation of the brake operating member is adapted to concurrently activate the brakes for the respective wheels, detect the deceleration value of the motor vehicle during the concurrent activation of the brakes, obtain the actual values of the braking torque values of. the brakes for the front and rear wheels on the basis of the detected vehicle deceleration value, and estimate the relationship on the basis of the obtained actual braking torque value of each brake.
In the braking system according to the above mode (22) wherein the brakes for the front and rear wheels are concurrently activated, the required time of activation of the brakes can be reduced as compared with the required time where the brakes are activated at different times.
Since the brakes for the front and rear wheels are concurrently activated, the vehicle deceleration value detected is influenced by both of the actual braking torque values of the front and rear brakes. However, the actual braking torque values of the front and rear brakes can be estimated by calculation based on the detected vehicle deceleration value, and the relationship for each of the front and rear wheels is estimated on the basis of the actual braking torque value obtained for each wheel, although the vehicle deceleration value detected during the concurrent activation of the front and rear brakes is influenced by the actual braking torque values of the respective brakes.
(23) An electrically operated braking system according to the above mode (6) or (7), further comprising first inhibiting means for inhibiting the relationship estimating and utilizing device from operating the brake to obtain the relationship while the motor vehicle is running under a condition in which the operation of the brake is likely to be felt unusual or uncomfortable by the operator of the motor vehicle.
In the braking system according to the above mode (23) of this invention, the actual braking torque of the brake during activation of the brake without an operation of the brake operating member can be obtained without the vehicle operator feeling unusual with the activation of the brake.
(24) An electrically operated braking system according to the above mode (23), wherein the first inhibiting means includes means for inhibiting the relationship estimating and utilizing device from operating the brake when the motor vehicle is running at a speed lower than a predetermined threshold.
In the braking system according to the above mode (24), the operation of the relationship estimating and utilizing device without an operation of the brake operating member is inhibited when the vehicle running speed is lower than the predetermined lower limit. This arrangement is based on a finding that the vehicle operator is more likely to feel unusual or uncomfortable with the activation of the brake during running of the vehicle at a relatively low speed, than at a relatively high speed.
(25) An electrically operated braking system according to the above mode (24), wherein said means for inhibiting the relationship estimating and utilizing device from operating the brake when the vehicle is running at a speed lower than a predetermined threshold includes vehicle speed detecting means for detecting the running speed of the vehicle, and inhibits the operation of the relationship estimating and utilizing means from operating to activate the brake when the detected vehicle running speed is lower than the predetermined threshold.
In the braking system according to the above mode (25), the vehicle speed detecting means may be adapted to directly detect the running speed of the vehicle. Alternatively, the vehicle speed detecting means comprises wheel speed sensors for detecting rotating speeds of respective wheels of the vehicle, and vehicle speed estimating means for determining as an estimated vehicle running speed a highest one of the wheel speeds detected by the respective wheel speed sensors on the basis of a fact that the highest wheel speed is closest to the actual running speed of the vehicle.
(26) An electrically operated braking system according to any one of the above modes (23)-(25), wherein said first inhibiting means comprises means for inhibiting the relationship estimating and utilizing means from operating the brake when the vehicle is turning.
In the braking system according to the above mode (26), the operation of the relationship estimating and utilizing means is inhibited during turning of the vehicle, based on a finding that the operation of the brake during turning of the vehicle is likely to cause the vehicle to have a behavior which is felt unusual or comfortable by the vehicle operator.
(27) An electrically operated braking system according to the above mode (26), wherein the means for inhibiting the relationship estimating and utilizing means from operating the brake when the vehicle is turning includes a vehicle turning sensor for detecting turning of the vehicle, and inhibits the operation of the relationship estimating and utilizing device to activate the brake when the turning of the vehicle is detected by the vehicle turning sensor.
(28) An electrically operated braking system according to any one of the above modes (1)-(27), further comprising second inhibiting means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship while the motor vehicle is running under a condition in which the relationship estimating and utilizing device is not likely to accurately estimate the relationship.
In the braking system according to the above mode (28), the relationship estimating and utilizing device is inhibited from at least utilizing the relationship while the motor vehicle is running under a condition in which the relationship estimating and utilizing device is not likely to accurately estimate the relationship. This arrangement is based on a finding that the relationship cannot always be estimated with high accuracy. Thus, the present arrangement assures increased reliability of the relationship estimating and utilizing device. Where the estimated relationship is utilized to control the brake, the relationship estimated in the above-indicated running condition of the vehicle is not utilized for controlling the vehicle, whereby the accuracy of control of the brake is improved.
(29) An electrically operated braking system according to the above mode (28) wherein the second inhibiting means includes means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship while a drive force for driving the motor vehicle is being changed.
In the braking system according to the above mode (28), the relationship estimating and utilizing device is inhibited from at least utilizing the relationship while the motor vehicle is running with a drive force being changed. This arrangement is based on a finding that the relationship is not likely to be estimated accurately while the drive force for driving the vehicle is being changed. The vehicle drive force may be changed due to a change in the output of a drive power source of the vehicle, or in the speed ratio of a power transmission of the vehicle as described below.
(30) An electrically operated braking system according to the above mode (29), wherein the motor vehicle includes a drive power source for driving the motor vehicle, and an accelerator operating member which is operated by the operator of the motor vehicle to increase an output of the drive power source for accelerating the motor vehicle, and wherein said means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship comprises means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship while said accelerator operating member is in operation.
In the braking system according to the above mode (30), the relationship estimating and utilizing device is inhibited from at least utilizing the relationship during operation of the accelerator operating member. This arrangement is based on a finding that the relationship is not likely to be estimated accurately while the accelerator operating member is in operation. The drive power source may be an engine such as an internal combustion engine, or an electric motor, or a combination of an engine and an electric motor.
The accelerator operating member may be considered to be xe2x80x9cin operationxe2x80x9d, when the accelerator operating member is placed in one of the following states: a first transient state in which the accelerator operating member is operated to increase the output of the drive power source to accelerate the motor vehicle; a steady state in which the accelerator operating member is held at the same position to maintain the output of the drive power source at the same value; and a second transient state in which the accelerator operating member is operated to reduce the output of the drive power source to decelerate the motor vehicle. However, the accelerator operating member may be considered to be xe2x80x9cin operationxe2x80x9d only when the accelerator operating member is placed in the first transient state, or in the first or second transient state. In other words, the relationship estimating and utilizing device may be inhibited from at least utilizing the relationship when the accelerator operating member is in one of the first and second transient states and the steady state, or in one of the first and second transient states, or in the first transient state.
The operating state of the accelerator operating member may be detected by either a switch for detecting whether the accelerator operating member is placed in a non-operated position or an operated position, or a position sensor capable of continuously detecting an amount of operation of the accelerator operating member from the non-operated position. The switch is usually used for detecting a moment at which the accelerator operating member is operated from the non-operated position to an operated position, or returned from the operated position to the non-operated position. However, this switch cannot detect a change in the operating position of the accelerator operating member, or the operating amount of the accelerator operating member. That is, while the switch is capable of detecting whether the accelerator operating member is in operation or not, but is not capable of detecting whether the accelerator operating member is placed in the first transient state (vehicle accelerating state) or the second transient (vehicle decelerating state), or held in the steady state (same operating position). On the other hand, the position sensor is capable of detecting whether the accelerator operating member is placed in the first transient or accelerating state or in the second transient or decelerating state. The above-indicated switch may be a switch for detecting an operation of an accelerator pedal as the accelerator operating member. The above-indicated sensor may be a sensor for detecting an amount of operation of the accelerator pedal, or a sensor for detecting an angle of opening of a throttle valve provided in an intake valve of an engine (internal combustion engine) which is provided as the drive power source. The throttle valve may be operated according to only an operation of the accelerator operating member, or according to selectively an operation of the accelerator operating member or a control command applied to an electrically operated throttle actuator provided for automatically operating the throttle valve. To accurately detect a change in the output of the engine, the throttle valve sensor for detecting the opening angle of the throttle valve is preferably used.
(31) An electrically operated braking system according to the above mode (29), wherein the motor vehicle includes an engine for driving the vehicle, and a fuel supply device for supplying a fuel to a combustion chamber of the engine, and wherein the means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship while the drive force for driving the engine is being changed comprises means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship when the fuel supply device is switched between an operated state thereof in which the fuel is supplied to the combustion chamber and a non-operated state thereof in which the fuel is not supplied to the combustion chamber.
In the braking system according to the above mode (31), the relationship estimating and utilizing device is inhibited from at least utilizing the relationship when the fuel supply device is switched between the operated and non-operated state. This arrangement is based on a finding that the relationship is not likely to be estimated accurately when the fuel supply device is switched between the operated and non-operated states.
In a certain type of motor vehicles, the fuel supply device may be switched between the operated and non-operated states, even while the accelerator operating member is not in operation. In this type of motor vehicle wherein the relationship is not likely to be estimated accurately due to a change in the output of the engine even while the accelerator operating member is not in operation, the arrangement according to the above mode (31) is effective to prevent utilization of the relationship estimated while the engine output is changing.
(32) An electrically operated braking system according to any one of the above modes (29)-(31), wherein the motor vehicle includes a drive power source, and a power transmission for transmitting the drive force of the drive power source to the wheel at a selected one of a plurality of speed ratios, and wherein the means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship comprises means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship while the power transmission is in the process of a shifting action to change the speed ratio.
In the braking system according to the above mode (32), the relationship estimating and utilizing device is inhibited from at least utilizing the relationship while the power transmission is in the process of a shifting action. This arrangement is based on a finding that the relationship is not likely to be estimated accurately in the process of a shifting action of the power transmission.
(33) An electrically operated braking system according to the above mode (32), wherein the means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship while the power transmission is in the process of a shifting action comprises a shift sensor for detecting the shifting action of the power transmission.
(34) An electrically operated braking system according to any one of the above modes (28)-(33), wherein the second inhibiting means includes means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship while the motor vehicle is turning.
In the braking system according to the above mode (34), the relationship estimating and utilizing device is inhibited from at least utilizing the relationship during turning of the vehicle. This arrangement is based on a finding that the relationship is not likely to be estimated accurately while the vehicle is turning.
(35) An electrically operated braking system according to the above mode (34), wherein the means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship while the motor vehicle is turning includes a vehicle turning sensor for detecting a turning of the motor vehicle.
(36) An electrically operated braking system according to any one of the above modes (28)-(35), wherein the second inhibiting means comprises means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship while the motor vehicle is running on a bad road surface.
In the braking system according to the above mode (36), the relationship estimating and utilizing device is inhibited from at least utilizing the relationship during running of the vehicle on a bad road surface This arrangement is based on a finding that the relationship is not likely to be estimated accurately while the vehicle is running of a bad road surface.
The bad road surface may be a graveled road surface, a Belgian brick- or stone-paved road surface, a non-paved road surface, or any other bumpy road surface.
(37) An electrically operated braking system according to the above mode (36), wherein the means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship while the motor vehicle is running on a bad road surface includes means for detecting the bad road surface.
(38) An electrically operated braking system according to any one of the above modes (28)-(37), wherein the second inhibiting means comprises means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship while a slip ratio of the wheel is higher than a predetermined threshold.
(39) An electrically operated braking system according to the above mode (38), wherein the means for inhibiting the relationship estimating and utilizing device from at least utilizing the relationship while the slip ratio of the wheel is higher than a predetermined threshold includes means for detecting that the slip ratio is higher than the predetermined threshold.
(40) An electrically operated braking system according to any one of the above modes (1)-(39), wherein said relationship estimating and utilizing device comprises braking torque obtaining means for obtaining the actual value of the braking torque for obtaining the actual value of the braking torque on the basis of a rate of change of the deceleration value of the motor vehicle or a rate of change of the deceleration value of the wheel.
Where the actual value of the braking torque of the brake is obtained on the basis of the deceleration value of the motor vehicle or the drive wheel, the obtained actual value of the braking torque is likely to be influenced by the overall drive force of the vehicle or the drive force of the drive wheel. Where the actual value of the braking torque is obtained on the basis of the rate of change of the vehicle or wheel deceleration value, the obtained actual value of the braking torque is relatively less likely to be influenced by the drive force. In the braking system according to the above mode (40), therefore, the actual value of the braking torque can be obtained with a reduced influence by the drive force of the vehicle or drive wheel.
(41) An electrically operated braking system according to any one of the above modes (1)-(40), wherein the brake includes a self-servo mechanism operated such that a friction force between the friction member and the rotor is increased by the friction force.
Referring to the graph of FIG. 8, there are indicated a plurality of I-T relationships between an electric current I (electric power) to be supplied to the electric motor and the braking torque T in the brake including a self-servo mechanism, which relationship correspond to respective different values xcexc of a friction coefficient of the friction member. It will be understood from the graph that the rate of increase of the braking torque T with an increase in the electric current I is higher when the friction coefficient xcexc of the friction member is relatively high than when it is relatively low. Where the brake includes the self-servo mechanism, therefore, the need of estimating the actual relationship between the electric power and the braking torque and utilizing the estimated relationship for controlling the brake is relatively high. This need is satisfied in the braking system according to the above mode (41), wherein the braking torque generated by the brake can be accurately controlled in relation to the operating amount of the brake operating member, even where the brake is provided with the self-servo mechanism.
(42) An electrically operated braking system according to the above mode (41), wherein the brake including the self-servo mechanism includes a drum brake which has brake linings as the friction member and a drum as the rotor.
(43) An electrically operated braking system according to the above mode (41) or (42), wherein the brake including the self-servo mechanism includes a disc brake which has brake pads as the friction member and a disc as the rotor.
(44) An electrically operated braking system according to any one of the above modes (1)-(39), wherein the relationship. estimating and utilizing device obtains the actual value of the braking torque on the basis of a change in a running condition of the motor vehicle due to the operation of the brake.
The xe2x80x9cchange in a running condition of the motor vehiclexe2x80x9d indicated above may include a change in the deceleration value of the motor vehicle.
(45) An electrically operated braking system according to any one of the above modes (1)-(39), wherein the relationship estimating and utilizing device comprises means for obtaining the actual value of the braking torque on the basis of a change in a rotating state of the wheel due to the operation of the brake.
The xe2x80x9cchange in a rotating state of the wheelxe2x80x9d indicated above may include a change of the deceleration value of the wheel, and a rate of change of the deceleration value of the wheel.
(46) An electrically operated braking system according to any one of the above modes (1)-(45), wherein the brake includes a support member for supporting the friction member in frictional contact with the rotor so as to prevent the friction member from being rotated with the rotor, and the relationship estimating and utilizing device includes a force switch which is interposed between the friction member and the support member, so as to receive a force from the friction member in frictional contact with the rotor, the force switch being selectively placed in one of two states, depending upon whether the force received from the friction member is larger than a predetermined threshold which is not zero, the relationship estimating and utilizing device utilizing an output of the force switch to obtain the actual value of the braking torque.
(47) An electrically operated braking system according to the above mode (46), wherein the rotor is a disc having a friction surface, and the friction member is a brake pad which is movable into frictional contact with the friction surface, the force switch being disposed in a position at which a spacing between the brake pad and the support member decreases with an increase in an amount of rotation of the brake pad with the disc.
(48) An electrically operated braking system according to the above mode (46) or (47), wherein the relationship estimating and utilizing device further includes a pressing-force-related quantity sensor whose output varies continuously with a quantity relating to a pressing force generated by the electric motor to force the friction member onto the rotor, the relationship estimating and utilizing device using the output of the pressing-force-related quantity sensor as a quantity relating to the actual value of the electric power supplied to the electric motor.
(49) An electrically operated braking system according to the above mode (48), wherein the relationship estimating and utilizing device further includes a braking force estimating device for estimating the braking torque to be applied to the wheel, on the basis of the output of the pressing-force-related quantity sensor and according to a predetermined relationship between the output and the braking torque, the braking force estimating device compensating the predetermined relationship on the basis of the output when the force switch is switched from one of the two states to the other states.
(50) An electrically operated braking system according to the above mode (49), wherein the braking force estimating device includes relationship compensating means for compensating the predetermined relationship, on the basis of a difference between an actual value of the output and a nominal value of the output when the force sensor is switched from one of the two states to the other.
(51) An electrically operated braking system of a motor vehicle having a wheel, comprising: (a) a rotor rotating with the wheel; (b) a brake operating member which is operated by an operator of the motor vehicle; (c) an electric power source; (d) a brake including a friction member movable to be forced onto the rotor, and an electric motor which is operated by an electric power supplied from the electric power source, to generate a drive force for forcing the friction member onto the rotor and thereby braking the wheel; and (e) a controller which determines an amount of the electric power to be supplied from the electric power source to the electric motor, depending upon an operating amount of the brake operating member, for thereby controlling an operation of the brake, the braking system characterized by further comprising (f) a relationship estimating and utilizing device for obtaining an actual value of a physical quantity relating to the electric power supplied from the electric power source to the electric motor during an operation of the brake while the motor vehicle is running, and an actual value of a physical quantity relating to a braking torque applied from the brake to the wheel during the operation of the brake, for estimating a relationship between the electric power to be supplied to the electric motor and the braking torque to be applied to the wheel, on the basis of the actual values obtained, and for utilizing the relationship, the relationship being formulated such that the braking torque to be applied to the wheel being changed with a change in the electric power to be supplied to the electric motor.
According to the present invention, there is also provided:
(52) An electrically operated brake for a motor vehicle having a wheel, comprising a rotor rotating with the wheel, a friction member movable to be forced onto the rotor, an electric motor operated to generate a drive force for forcing the friction member onto the rotor, and a self-servo mechanism which is operated such that a friction force between the friction member and the rotor is increased by the friction force, the electrically operated brake being characterized by further comprising a biasing mechanism interposed between the friction member and a stationary member which supports the friction member, the biasing mechanism biasing the friction member in a direction for moving the friction member away from the rotor.
In an electrically operated brake provided with a self-servo mechanism, there is a general tendency that the friction member cannot be moved away from the rotor with a high response to a command generated to return the electric motor to its initial position, once the self-servo mechanism is activated to provide a self-servo effect. Therefore, the braking torque cannot be rapidly reduced to zero. In the brake according to the above mode (52) in which the biasing mechanism is provided, the biasing mechanism is effective to rapidly move the friction member away from the rotor, thereby permitting rapid reduction of the braking torque.
The biasing mechanism may be adapted to hold the friction member in the biased state, or bias the friction member only when it is required to rapidly reduce the braking torque.
(53) A braking system for a motor vehicle having a wheel, comprising: (a) a rotor rotating with the wheel; (b) a friction member movable to be forced onto the rotor, for braking the wheel; (c) a support member for supporting the friction member in frictional contact with the rotor so as to prevent the friction member from being rotated with the rotor; (d) a pressing device for forcing the friction member into frictional contact with the rotor; and (e) a force switch which is interposed between the friction member and the support member, so as to receive a force from the friction member in frictional contact with the rotor, the force switch being selectively placed in one of two states, depending upon whether the force received from the friction member is larger than a predetermined threshold which is not zero.
The braking system constructed according to the above mode (53) of this invention provides an improvement over a conventional braking system which uses a braking-force-related quantity sensor for continuously detecting a physical quantity relating to braking force generated by a brake. This sensor may be a strain gage using an electrically resistive wire, or a piezoelectric sensor. The quantity which is detected by the sensor and which relates to the braking force changes over a relatively wide range. Accordingly, it is generally difficult for the sensor to detect the quantity with high accuracy over the entire range. Further, the operating environment of the sensor is considerably severe. Namely, the sensor may be subject to a considerable amount of change in the operating temperature and a considerably intense vibration, and is likely to be exposed to foreign matters such as mud, water and dust or grit. Thus, the braking-force-related quantity sensor used in the conventional braking system is not capable of detecting a quantity relating to the braking force, with a high degree of reliability, and does not have a satisfactory degree of durability.
The force switch used according to the above mode of the present invention is different from a sensor in that like a commonly used switch, the force switch is not capable of continuously detecting a physical quantity. However, the force switch is less likely to be influenced by the operating environment, as compared with a sensor, since the force switch is simpler in construction and operating principle. For instance, a relationship between the actual value of the physical quantity and the output of the force sensor is less likely to be influenced by the operating environment, that a relationship between the actual value of the quantity and the output of a sensor. Accordingly, the force switch is capable of detecting, with high reliability and durability, whether the force which the support member receives from the friction member as a physical quantity relating to the braking force has exceeded the predetermined value or has been reduced to the predetermined value.
(54) A braking system according to the above mode (53), wherein the rotor is a disc having a friction surface, and the friction member is a brake pad which is movable into frictional contact with the friction surface, the force switch being disposed in a position at which a spacing between the brake pad and the support member decreases with an increase in an amount of rotation of the brake pad with the disc.
(55) A braking system according to the above mode (1) or (2), wherein the force switch is provided at each of a plurality of positions between the friction member and the support member, and the force switches at the different positions have respective different predetermined threshold values of the force received from the friction member.
In the braking system according to the above mode (55), the quantity relating to the braking force can be detected in two or more steps by the respective force sensors.
(56) A braking system according to any one of the above modes (53)-(55), wherein the force switch includes a pair of contacts which are movable relative to each other between two positions corresponding to the above-indicated two states, and one of the contacts is fixed to the friction member while the other contact is fixed to the support member.
The force switch in the braking system according to the above mode (56) is relatively simple in construction and operating principle, and accordingly assures increased operating reliability and durability.
(57) A braking system according to the above mode (56), wherein the contact fixed to the friction member is a movable contact, while the contact fixed to the support member is a stationary contact.
(58) A braking system according to any one of the above modes (53)-(57), wherein the pressing device includes an electric motor as a drive source, and does not use a pressurized hydraulic fluid.
(59) A braking system according to any one of the above modes (53)-(57), wherein the pressing device uses a pressurized hydraulic fluid.
(60) A braking system according to any one of the above modes (53)-(59), wherein the friction member, support member, pressing device and force switch cooperate to constitute a major portion of a brake, the braking system further comprising a brake information obtaining device for obtaining brake information relating to an operation of the brake.
In the braking system according to the above mode (60), the brake information may include a friction coefficient of the friction member, information as to whether the friction coefficient of the friction member is unacceptably low or not, information as to whether the brake is abnormal, and a friction coefficient between the Wheel and the road surface.
(61) A braking system according to any one of the above modes (53)-(59), further comprising: a pressing-force-related quantity sensor whose output varies continuously with a quantity relating to a pressing force by which the friction member is forced onto the rotor by the pressing device; and a friction coefficient estimating device for estimating a friction coefficient of the friction member, on the basis of a relationship between the output of the pressing-force-related quantity sensor and the predetermined threshold.
In the braking system according to the above mode (61), the friction coefficient of the friction member can be estimated by the friction coefficient estimating device, so that the braking system can be controlled with high accuracy, by utilizing the estimated friction coefficient.
(62) A braking system according to the above mode (61), wherein the pressing device includes a presser member which is disposed on one of opposite sides of the friction member remote from the rotor, so as to force the friction member onto the rotor, and the pressing-force-related quantity sensor includes a pressing-force sensor provided on the presser member to continuously detect a force which acts on the presser member in a direction of movement of the presser member toward the friction member.
(63) A braking system according to the above mode (61), wherein the pressing device includes an electric motor for forcing the friction member onto the rotor, and the pressing-force-related quantity sensor includes an electric power sensor for continuously detecting an amount of electric power supplied to the electric motor.
(64) A braking system according to the above mode (63), wherein the electric power sensor is a motor current sensor for continuously detecting an amount of electric current supplied to the electric motor.
(65) A braking system according to any one of the above modes (61)-(64), wherein the above-indicated two states of the force sensor consists of an on state and an off state, the state of the force switch being changed from one of the on and off states to the other when the force received from the friction member has increased and exceeded the above-indicated predetermined threshold, and is changed from the above-indicated other state to the above-indicated one state, and wherein the friction coefficient estimating device estimates the friction coefficient of the friction member when at least one of a change from the above-indicated one state to the other state and a change from the above-indicated other state to the above-indicated one state takes place.
(66) A braking system according to the above mode (65), wherein the friction coefficient estimating device estimates the friction coefficient of the friction member when each of the changes between the on and off states takes place.
In the braking system according to the above mode (66), the friction coefficient is estimated at the two opportunities, namely, when the force switch is turned on and when the force switch is turned off. Accordingly, the accuracy of estimation of the friction coefficient can be improved, as compared with the accuracy of estimation where the friction coefficient is estimated only once, that is, when the force switch is turned on or turned off.
(67) A braking system according to any one of the above modes (61)-(66), wherein said friction coefficient estimating device estimates the friction coefficient of the friction member, by dividing the above-indicated predetermined threshold by the quantity as detected by the pressing-force-related quantity sensor when the state of the force switch is changed from one of the above-indicated two states to the other.
(68) A braking system according to any one of the above modes (61)-(67), further comprising a brake pad fade detecting device for detecting that the friction coefficient estimated by the friction coefficient estimating device is lower than a predetermined lower limit.
(69) A braking system according to any one of the above modes (53)-(59), wherein the friction member, support member, pressing device and force switch cooperate to constitute a major portion of a brake, the braking system further comprising: a physical quantity sensor for detecting a physical quantity which relates to an operation of the brake and which excludes a force acting on the force switch, the physical quantity changing in relation to the force acting on the force switch, depending upon whether the brake is abnormal or not; and a brake failure detecting device for detecting whether the brake is abnormal or not, on the basis of a relationship between an output of the physical quantity sensor and an output of the force switch.
(70) A braking system according to any one of the above modes (53)-(59), wherein the friction member, support member, pressing device and force switch cooperate to constitute a major portion of a brake, the braking system further comprising a road surface friction coefficient estimating device for estimating a friction coefficient between the wheel and a road surface on which the motor vehicle is running, on the basis of an output of the force switch.
(71) A braking system according to any one of the above modes (53)-(70), wherein said pressing device includes an electric motor for forcing the friction member onto the rotor, and cooperates with the rotor, friction member, support member and force sensor to constitute an electrically operated brake, the braking system further comprising a mechanically operated brake which is operated mechanically to brake the wheel by a force generated by a manually operated brake operating member, and a manual brake control device disposed between the mechanically operated brake and the brake operating member, for permitting an operation of the mechanically operated brake when the electrically operated brake is abnormal, and inhibiting the operation of the mechanically operated brake when the electrically operated brake is normal.
In the braking system according to the above mode (71), the electrically operated brake is used as a normal brake, and the mechanically operated brake is used as an emergency brake which is activated by the force generated by the brake operating member. Thus, the present braking system is provided with an electrically operated sub-system including the brake operating member and the electrically operated brake, and a mechanically operated sub-system including the brake operating member, the manual brake control device and the mechanically operated brake. Therefore, the present braking system is capable of braking the wheel with the braking force corresponding to the operating force acting on the brake operating member, even when the electrically operated brake is abnormal or defective. Accordingly, the present braking system has increased operating reliability and improved safety of the vehicle.
In the present braking system, the mechanically operated brake and the manual brake control device may or may not use a pressurized hydraulic fluid.
The electrically operated brake may be adapted to be operated according to an intention of the vehicle operator, which is represented by an operation of the brake operating member. For instance, the electrically operated brake may be operated according to the operating force acting on the brake operating member, or the operating amount or stroke of the brake operating member.
In the present braking system, the friction member and the rotor may be commonly used for the electrically and mechanically operated brakes. Alternatively, the electrically and mechanically operated brakes may use respective sets of the friction member and rotor.
(72) A braking system according to the above mode (71), further comprising a brake information obtaining device for obtaining information relating to the electrically operated brake, on the basis of an output of the force switch, and wherein the brake information obtaining device is inhibited from operating when the manual brake control device is operated.
In the braking system according to the above mode (72), the information relating to the electrically operated brake includes information which has been described above with respect to the above mode (60).
(73) A braking system according to any one of the above modes (53)-(59), wherein the friction member, support member, pressing device and force switch constitute a major portion of a brake, the braking system further comprising: a force-related quantity sensor whose output varies continuously with a quantity relating to one of a braking force generated by the brake and applied to the wheel and a pressing force generated by the pressing device to force the friction member onto the rotor; a wheel braking force estimating device for estimating the braking torque to be applied to the wheel, on the basis of the output of the force-related quantity sensor and according to a predetermined relationship between the output and the braking torque, the wheel braking force estimating device compensating the predetermined relationship on the basis of the output when the force switch is switched from one of the two states to the other state.
It will be understood from the foregoing description that the force switch is advantageous for its comparatively high operating reliability but is disadvantageous for its incapability of continuous detection of the force, while on the other hand the force-related quantity sensor is advantageous for its capability of continuous detection of the force-related quantity but is disadvantageous for its comparatively low operating reliability. Thus, the force switch and the force-related quantity sensor mutually supplement their disadvantages, cooperating with each other to permit continuous detection of the force-related quantity with high reliability. The braking system according to the above mode (73) is based on this finding.
Where the force-related quantity sensor in the braking system according to the above mode (73) is a pressing-force-related quantity sensor adapted to continuously detect a quantity relating to the pressing force generated by the pressing device, the quantity detected by this pressing-force-related quantity sensor is not influenced by a variation in the friction coefficient of the friction member, but the output of the force switch is influenced by the variation. In this case, the wheel braking force estimating compensates the above-indicated relationship by taking account of both the variation in the operating characteristic of the pressing-force-related sensor and the variation in the friction coefficient of the friction member. Where the force-related quantity sensor is a braking-force-related quantity sensor adapted to continuously detect a quantity relating to the braking force applied to the wheel, the force detected by the force switch and the quantity detected by the braking-force-related quantity sensor are substantially the same physical quantities which are not influenced by the variation in the friction coefficient of the friction member. In this case, the wheel braking force estimating device compensates the above-indicated relationship by adjusting the calibration of the braking-force-related quantity sensor.
The above-indicated relationship may be either directly compensated, or indirectly or eventually compensated. In the latter case, the output of the force-related quantity sensor may be compensated, or alternatively the wheel braking force provisionally estimated may be compensated on the basis of the output of the sensor and the predetermined relationship.
(74) A braking system according to the above mode (73), wherein the force-related quantity sensor includes a pressing force sensor whose output continuously varies with the pressing force acting thereon.
The operating environment of the pressing force sensor is not so severe as compared with that of the a braking force sensor which will be described. In the braking system according to the above mode (74), therefore, the operating reliability and durability of the pressing force sensor can be relatively easily improved.
(75) A braking system according to the above mode (73), wherein the force-related quantity sensor includes a braking force sensor whose output continuously varies with the force which the support member receives from the friction member as the braking force applied to the wheel.
(76) A braking system according to any one of the above modes (73)-(75), wherein the wheel braking force estimating device includes relationship compensating means for compensating the predetermined relationship, on the basis of a difference between an actual value of the output and a nominal value of the output when the force sensor is switched from one of the two states to the other.
(77) A braking system according to the above mode (76), wherein the relationship compensating means compensates the predetermined relationship such that the pressing force obtained on the basis of the actual value of the output of the braking force sensor coincides with the actual value of the pressing force, even in the presence of the above-indicated difference.
(78) A braking system according to any one of the above modes (73)-(77), further comprising a brake information estimating device for obtaining brake information relating to an operation of the brake, on the basis of the output of the force switch.
The brake information estimating device and xe2x80x9cbrake information relating to an operation of the brakexe2x80x9d in the above mode (78) are similar to those which have been discussed above with respect to the above mode (60) of this invention.
(79) A braking system according to the above mode (78), wherein the brake information estimating device includes a friction coefficient estimating device for estimating a friction coefficient of the friction member, on the basis of a relationship between the output of the brake-related quantity sensor and the above-indicated predetermined threshold of the force switch when the force switch is switched from one of the two states to the other.
The friction coefficient estimating device according to the above mode (79) is similar to that which has been discussed above with respect to the above mode (61).